Anthony Weiner, right, with Christine Quinn, Democratic Mayoral Candidates at an event at Hunter College. A new poll from Quinnipiac University shows a virtual dead heat between Quinn, Weiner and Bill Thompson Photo: Stephen Yang

The mayor’s race – once Christine Quinn’s to lose – has turned into a virtual dead heat among the top three contenders, according to a poll released today.

After leading the pack at 37 percent in February, Quinn has dropped steadily to 19 percent in the latest Quinnipiac University survey, with Anthony Weiner and Bill Thompson hot on her trail at 17 and 16 percent , respectively.

Public Advocate Bill de Blasio held steady at 10 percent and Comptroller John Liu – dogged by a federal investigation into his campaign finances year – was struggling at 7 percent.

The poll was the biggest surge of the campaign for Thompson, who has always been viewed as a formidable candidate by political insiders but has had trouble breaking double digits.

The endorsement from the United Federation of Teachers last week undoubtedly helped Thompson, said poll director Mickey Carroll.

“The big story in my book is Thompson,” Carroll said. “I think the UFT moved Thompson up and I guess the second story is Quinn down and Weiner up. You can explain Thompson. The Quinn-Weiner stuff is harder to explain.”

In a Marist College/Wall Street Journal/NBC-TV poll out Tuesday night, Weiner led Quinn 25 to 20 percent, with Thompson at 13 percent.

Carroll sought to explain the discrepancy by noting that Quinnipiac polled after the UFT endorsement, but Marist finished surveying voters days earlier.

Among other things, Marist poll chief Lee Miringoff said his questioners asks undecided voters how they’re leaning; something he said Quinnipiac doesn’t do.

Twenty-eight percent of the 1,238 registered Democrats surveyed were still undecided in the new poll.

Both Quinn’s and Thompson’s campaigns downplayed the results.

“In the course of 24 hours two separate polls have shown two separate things. The one thing that is constant is that Christine Quinn is the only candidate who has demonstrated she can lead this city,” said Quinn spokesman Mike Morey.

“We’re not going to make a fuss about early polls when they’re good for us or bad for us, because they’re all early polls. This race will be decided in late summer, and one of the people on the other end of it will be Bill Thompson – who is always underestimated and who always closes strong,” said Thompson strategist Jonathan Prince said.

Meanwhile Weiner’s strong showing in the Marist poll turned him into a target for GOP mayoral candidate Joe Lhota.

“I’m sure that you had hoped to have seen the last of Anthony Weiner when he resigned from Congress following an illicit sexual Twitter scandal and botched cover up but he’s back and desperate for political redemption,” Lhota wrote in a fund-raising e-mail to supporters.